Azadirachta indica (Neem) gum was effectively used in the combustion process as the sustainable fuel for the synthesis of ZnO nanoparticles using zinc nitrate as the metal precursor. Thermal degradation of gum intermediate, which contains uniformly distributed Zn ions in gum matrix, by means of exothermic combustion reaction results in the formation of ZnO nanoparticles at a relatively lower temperature of 220∘C. Further, the phase stabilization of ZnO nanoparticles was performed at 700∘C for 3[Formula: see text]h in ambient condition, which also led to the complete removal of organic residues. FTIR, XRD, SEM-EDX and TEM characterization of the ZnO nanoparticles reveals its phase purity and organic-free nature with a size ranging between 40 and 60[Formula: see text]nm. Its optical activities were studied by UV–Visible and photoluminescence studies and the UV–Visible analysis reveals its band gap energy as 3.17[Formula: see text]eV. Further, the synthesized ZnO nanoparticles showed splendid germicidal activity against Staphylococcus aureus (gram-positive bacteria), Escherichia coli (gram-negative bacteria) and Candida albicans (fungal pathogen). In addition, the bio-synthesized ZnO nanoparticles showed excellent antioxidant behavior with the 81% of free radical quenching while employing 100[Formula: see text][Formula: see text]g/mL nanoparticle concentration.